1. Field of the Invention
This invention relates to a process for producing pryidine by the oxidative dealkylation of alkylpyridines or alkenylpyridines.
2. Description of the Prior Art
Various synthetic methods have been developed for producing pyridine bases, and the production of pyridine bases has already been performed commercially. Current commercial methods for producing pyridine bases, however, yield fairly large amounts of akylpyridines in addition to pyridine. The consumption of pyridine as a raw material for agricultural chemicals, etc. has recently increased, and an imbalance has arisen in the supply and demand between pyridine and alkylpyridines. Hence, attention has been diverted to methods for producing pyridine which do not involve the formation of alkylpyridines, and further to methods for producing pyridine by affirmatively dealkylating alkylpyridines.
The production of pyridine by dealkylation of alkylpyridines is known (e.g., as described in U.S. Pat. Nos. 2,504,172, 3,335,144 and 3,334,101), and various processes have been investigated. Most of these dealkylating methods are hydrogenating dealkylation methods using hydrogen. However, since hydrogenating dealkylation requires a reaction apparatus capable of withstanding pressure, an oxidative dealkylation which can be performed in a reaction apparatus at normal atomospheric pressure is simpler in terms of the reaction equipment involved. However, only a few prior art techniques involving an oxidative dealkylation in the presence of a gas containing oxygen are known (e.g., as described in Latv. PSR Zinat. Akad. Vestis, Khim. Ser. (5) P559 (1969), Vopr. Khim, Khim. Tekhnol. vol 30, P140 (1974) and J. Appl. Chem. Bietechnol vol 26, P375 (1976)).
The method disclosed in British Pat. No. 1,191,913, which also is a prior art method for dealkylating alkylpyridines in the presence of an oxygen-containing gas, is characterized by using a vanadium-chromium type catalyst (optionally containing Cd, Bi, Ni, or Co as a promotor). When in this method, .alpha.-picoline, steam and air are used in a molar ratio of 1:20:15, the conversion of .alpha.-picoline is 94%, and the yield of pyridine is 63.7%. However, when the .alpha.-picoline is replaced by .beta.-picoline, the conversion of the .beta.-picoline is 75%, and the yield of pyridine is as low as 40.6%. Likewise, with .gamma.-picoline, the conversion is 87% and the yield is 56.8%. None of these results are satisfactory.
British Pat. No. 1,152,878, on the other hand, discloses a binary-element catalyst composed of an oxide of Cr, Co or Ag and V.sub.2 O.sub.5 supported on alumina as a catalyst for producing cyanopyridine by ammonxidation of alkylpyridines. The disclosure further is that by selecting the reaction conditions in the ammonxidation of an alkylpyridine with a V-Cr type catalyst, pyridine is obtained from .alpha.-picoline at a selectivity of 66.5%. However the method disclosed in British Pat. No. 1,152,878 is not satisfactory as a process for producing pyridine by dealkylation because ammonia is used in the reaction, cyanopyridine is formed simultaneously, and the reaction results are not satisfactory. In addition, no specific technical disclosure with respect to alkylpyridines other than .alpha.-picoline is given in this patent.